never mind, i got it! i figured out that at the top of the pendulum, centripetal force had to be equal to the force of gravity because there is no tension to support the bob.
Homework Statement
diagram: http://goo.gl/uPl0
Part A
A bullet of mass 0.0175 kg and speed vb passes completely through a pendulum bob of mass 1.3 kg. The bullet emerges with a speed 0.5vb. The pendulum bob is suspended by a stiff rod of length 1.1 m and negligible mass. The acceleration of...